This project is concerned with elucidating the primary structures of the amino acyl-tRNA syntheses, and identifying functional groups of these enzymes which are essential for activity. One example of this family of enzymes, isoleucyl-tRNA synthetase of E. coli, is currently being studied in detail. These studies are primarily concerned with amino acid sequence analysis, but the effects of some chemical modifications of the native enzyme are also being examined. When progress on this enzyme is significant, the study will be expanded to include comparative studies of other amino acyl-tRNA synthetases.